The manufacture of multi-chip modules (MCM), high-density interconnect (HDI) components and other semiconductor materials requires the application of a thin layer of polyamide material as an inner layer dielectric. The polyamide material must be filtered and then applied with exacting precision because the required thicknesses of the polyamide film may be as small as 100 microns and the final thickness of the polyamide film must be uniform and not normally vary more than 2% across the substrate or wafer.
In this connection, numerous problems arise with the construction and operation of a pump/filter apparatus that will supply polyamide material in exacting amounts and in a timely manner.
In addition to the unique mechanical and electrical properties that make polyamides ideally suited for use in the manufacture of semiconductors, polyamides also have physical properties that make it difficult to pump or supply the polyamides in exacting amounts. Specifically, polyamides are viscous; most polyamides used in the manufacture of semiconductors have viscosities in excess of 400 poise. Fluids with viscosities this high are difficult to pump and difficult to filter. Pumping a viscous fluid through a submicron filter can create high back pressures at the filter element.
Further, the viscosity of polyamide fluids can vary with time and temperature. Essentially, polyamide fluids must be date coded and viscosity measurements are valid for only relatively short periods of time, perhaps 10 days. It is known in the art that recirculation of polyamide fluids helps stabilize the viscosity. However, because polyamide fluids are viscous and the viscosity of the polyamide fluids is dependent on temperature, excessive recirculation may increase the temperature of the fluid and thereby alter the viscosity. Of course, changes in the fluid viscosity will affect the operation and performance of pumps used to dispense the fluid.
Pumps used in dispensing polyamide fluids must also be precise because of the high cost of the fluids. It is not uncommon for polyamide fluids to cost in excess of $15,000 per gallon. Therefore, it is important that pump systems used to dispense the polyamide fluids dispense the exact amounts, without waste.
At least three techniques are used for applying polyamide films to substrates during the manufacture of semiconductors. Those methods include applying a drop of polyamide material to the center of a substrate wafer following by rotation of the wafer to evenly distribute the polyamide across the wafer. However, in this system, a substantial amount of polyamide liquid is spun from the wafer and then discarded, resulting in loss of the expensive polyamide liquid. A second method includes the deposit of polyamide liquid on a rotating wafer. In this method, the dispense rate and amount must be tightly controlled so that the dispense pattern is consistent from one wafer to the next.
A third and more recent method is known as liquid extrusion. In this method, an exacting amount of polyamide liquid is applied to the wafer in a single pass. It is anticipated that liquid extrusion systems or similar methods will eventually replace the aforenoted methods that include rotation of the wafers.
The polyamide liquids are dispensed with pumps such as the ones shown in U.S. Pat. Nos. 5,167,837 and 4,950,134. The present invention provides a substantial contribution to the art of precision fluid pumping and to the designs disclosed in U.S. Pat. Nos. 5,167,837 and 4,950,134 by providing a reservoir disposed between the two pumps and further by providing an improved control system and recirculation system. Additionally, the diaphragm pumps disclosed in both U.S. Pat. Nos. 5,167,837 and 4,950,134 are prone to inaccuracies due to stretching of the diaphragm during operation of the pumps.
During the dispense and reload strokes of a diaphragm pump, pressure is exerted on the diaphragm causing the diaphragm to stretch. At the end of the dispense or reload stroke, some residual resilience exists in the rubber material comprising the diaphragm. This residual resilience can cause unwanted forces to be exerted on the fluid in the system. These forces cause small displacements of fluid leading to pump inaccuracies. The present invention provides a solution to this problem by pre-stressing the pump diaphragm to its maximum size during manufacture of the diaphragms, thereby reducing or eliminating residual resilience in the diaphragm.
Thus, the present invention is directed to improved dual-stage pumps systems for the precise dispensing of polyamide fluids and other viscous fluids that includes a separate reservoir disposed between the two pump units, a recirculation system and pre-formed pump diaphragms for enhanced pump accuracy.